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Some buildings in the besieged rebel stronghold of Sloviansk have been damaged by shelling

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Some of Sloviansk's population has fled the fighting

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Residents of Sloviansk have been queuing for rations

On Wednesday the Ukrainian military accused the rebels of breaking the ceasefire 44 times since it began.

But Alexander Borodai, prime minister of the self-styled Donetsk People's Republic, has said there is effectively no ceasefire because of government attacks.

The truce is part of Ukraine's plan to end two months of conflict with pro-Russian insurgents who control key buildings in towns and cities across the east.

More than 420 people have been killed in the region since mid-April, the UN estimates.

Analysis: David Stern, BBC News, Kiev

One would suspect that the Ukrainian government's truce in the east is now a dead letter. Public outrage alone would seem to demand some sort of military retaliation.

And if the Ukrainian government uses force, then very likely the Ukrainian insurgents and their Russian comrades-in-arms will answer in kind. An escalation seems inevitable.

At this point, it is close to impossible to determine why the militants decided to carry out such a provocative act, just one day after they declared a ceasefire. Maybe this was some rogue element. Maybe the insurgents were never serious. Maybe Moscow told them to do it.

Whatever the reason, the hopes of just 24 hours ago, that Ukraine's east could finally see peace, if only temporarily, ring especially hollow.